FOCAL HYPEREXPRESSION OF HEMEOXYGENASE-1 PROTEIN AND MESSENGER-RNA INRAT-BRAIN CAUSED BY CELLULAR STRESS FOLLOWING SUBARACHNOID INJECTIONSOF LYSED BLOOD

Induction of the hemeoxygenase-1 (ho-1) stress gene is of Importance f or rapid henze metabolism and protection against oxidative injury in v itro and in vivo. Although ho-1 expression is observed in glia followi ng exposure to whole blood and oxyhemoglobin, expression is mild, and other stress genes are not induced simultaneously in this setting. Hem eoxygenase-1 can be induced by several other physiological stresses in addition to heme. In the brain, ho-1 induction has been observed in t he penumbra following focal cerebral ischemia. Because lysed blood is a spasmogen, the authors studied focal hyperexpression of the ho-1 gen e after injection oi-lysed blood, whole blood, or saline into the cist erna magna or adult rats. Immunocytochemical analysis of HO-1 was perf ormed at 1, 2: 3, and 4 days after the injections. Because the 70-kD i nducible heal shock protein (HSP70) is induced by cellular stress, alt ernate sections were immunostained For HSP70 to assess whether focal h yperexpression was a stress phenomenon. An oligonucleotide probe was a lso used for in situ hybridization to demonstrate that ho-l messenger (m)RNA was present. Focal HO-1 immunostained areas were observed after lysed blood injection only and were located mainly in the basal corte x and cerebellar hemisphere. although focal hyperexpression was also f ound in many other regions. The intensity of staining and the number o f regions were maximum at 1 day, Double-labeled immunofluorescence rev ealed that many HO-1-immunoreactive cells were microglia. The HSP70 im munostaining of adjacent sections from the same animals demonstrated f ocal regions of immunoreactivity whose topography corresponded exactly with the topog raphy of the HO-1-immunostained areas. Conventional hi stology in regions of HO-1 hyperexpression was often normal. In situ h ybridization using the same oligonucleotide demonstrated that ho-1 mRN A was induced in focal areas of forebrain and in large regions of cere bellum within 6 hours of injection. These results demonstrate that foc al hyperexpression of the ho-1 stress gene occurs after lysed blood in jection and appears to be an indicator of cellular stress and injury i n regions in which infarction does not occur. These results also sugge st that cellular injury that occurs after injection of lysed blood may go undetected using conventional histology. Although direct heme meta bolism was not investigated, our results indicate that rapid metabolis m of heme, both intracellular and extracellular, may prove to be benef icial alter subarachnoid hemorrhage.